Emerson 2468CD 2.3.1INPUT BOARD PCB 24680501 AND PCB, 2.3.1.1Analogue Output Drive Capability

Hydrastep 2468CB and 2468CD Manual 2468CB & 2468CD Dual Power Supply Version

2.3.1INPUT BOARD (PCB 24680501 AND PCB 24680516)

The input board processes the electrode inputs to provide water level data for display purposes and a current output representing the water level. Fault detection is also carried out where the condition of the electrode inputs are examined and a FAULT is indicated when:

1.An open circuit in either of the electrode conductor cores is present.

2.A short circuit to EARTH on either the electrode or conductor cores.

3.A water above steam condition exists.

4.An internal circuit fault condition exists.

A current output circuit is also provided on each input board. This gives an analogue representation of the water level. The sense (forward or reverse) and type (0-20mAor

4-20mA) is selectable and described in Section 2.5 of this chapter. Fault indication on the analogue output is an oscillating waveform (of approximately 0.5 Hz) superimposed on the main analogue signal.

The electrode inputs to each input board are passed to the other input board so that each analogue circuit can output the full range content of electrode input signals. However, should either of the input boards fail, the remaining board recognises that data is missing and doubles its own electrode input signal to remedy the data loss giving a maximum error of

± 1 electrode.

Provision is made on each input board to accept one or two output boards, either relay outputs or opto-isolated outputs. Both types of output board are offered as options.

Each input board produces the power supplies for the whole instrument which are derived either from the local mains voltage supply of 110V ac or 240V ac nominal for the 24680501 input board or 20V dc to 40V dc for the 24680516 input board.

Apart from the input voltage there are two other differences between the AC (24680501) and DC (24680516) input boards. These are the analogue output drive capability and the remote display drive capability.

2.3.1.1Analogue Output Drive Capability

With the minimum DC supply voltage of 20V for the DC input board (24680516) the maximum load that can be driven by the analogue output is 500Ω.

At the minimum mains input voltage the AC input board (24680501) the maximum load that can be driven by the analogue output is 600Ω.

2.3.2REMOTE DISPLAY DRIVE CAPABILITY

The remote display drive capability is only a consideration when the 2468C is providing power for a remote display. With either input board the unit is capable of driving six remote displays at up to 1000m (3280ft) from the unit but only powering one remote display (any others must be locally powered). With the AC input board the maximum cable loop resistance to the remote display is 27Ω whilst with the DC input the maximum cable loop resistance to the remote display is 7Ω. (See remote display section for more details).

24685034 2-5